The incorporation of electronic devices with tire structures has been shown to yield many practical advantages. Piezoelectric devices have been incorporated with tire patches to provide a power source for various sensors and other components of a tire mountable apparatus used to measure tire parameters. Piezoelectric devices have also been used to acquire data, such as piezoelectric signals indicative of the time-varying shape of a rolling tire at the location of the piezoelectric device. The piezoelectric signals can be analyzed to assess various parameters of a tire. Such information may be useful in tire monitoring and warning systems as well as in tire testing and design.
One exemplary structure for a piezoelectric device can include a substrate having one or more piezoelectric components, such as a power generation component and a signal generation component. The power generation component can provide energy upon flexure of the power generation component to power various components of a tire mountable apparatus, such as temperature and pressure transducers used to monitor temperature and pressure of a tire. The signal generation component can provide signals, such as piezoelectric waveforms, associated with flexure of the signal generation component induced by the time-varying shape of the rolling tire. The signals generated from the signal generation component can be analyzed, for instance, to count tire revolutions, to determine tire speed, and to identify the contact patch angle for the tire.
WO 2010/024819 discloses a tire mountable apparatus including a piezoelectric substrate that has length and width dimensions for providing enhanced endurance of the tire mountable apparatus. The piezoelectric substrate can be mounted in a tire with a lateral orientation such that a line perpendicular to the direction of the length of the piezoelectric substrate is aligned substantially in the direction of rotation of the tire so that strain on the tire mountable apparatus is essentially limited to one direction.
While lateral orientation of the tire mountable apparatus can provide increased durability, it can negatively affect the nature of the signal shape of piezoelectric signals generated by the piezoelectric device. In particular, in certain tires, such as high aspect ratio tires, the lateral orientation of the tire mountable apparatus provides increased coupling of the piezoelectric device with changing lateral tire shape at the edges of the contact patch. The increased coupling with changing lateral tire shape can lead to distortions in signal shape of the piezoelectric signal from the piezoelectric device. These distortions can reduce the ability to extract accurate information from the piezoelectric signal, such as contact patch entry and exit times, tire revolution count, tire speed, and contact patch angle.